Here is the full list of all 50 Spec Ops: The Line achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Complete game on "FUBAR" difficulty.
Complete any chapter with 60%+ accuracy without dying or reloading a checkpoint.
Complete game on "Suicide Mission" difficulty.
Recover all Intel Items.
Kill 10 enemies while they use zip lines or are rappelling. (campaign only)
You are relieved.
Choose vengeance.
Follow your orders.
Show mercy.
Play it smart.
Blow up 10 explosive objects, killing at least one enemy each time. (campaign only)
Live and let die.
Live and let live.
Complete game on "Walk on the Beach" difficulty.
Complete game on "Combat Op" difficulty.
Carry on, soldier.
The end of the line.
Kill 50 enemies using only the Attack Command. (campaign only)
Kill 150 enemies with any heavy weapon. (campaign only)
Kill 50 enemies with grenades. (campaign only)
Choose restraint.
Kill 250 enemies with headshots. (campaign only)
Get out of here!
Kill 100 enemies with any pistol or SMG. (campaign only)
Hit 10 enemies with your melee attack. (campaign only)
Kill 50 enemies with any sniper rifle. (campaign only)
Recover 12 Intel Items.
Stun an enemy by dumping sand on their head. (campaign only)
Stand united.
Kill 350 enemies with any rifle. (campaign only)
Kick an enemy by vaulting over a cover. (campaign only)
Kill an oryx. (campaign only)
Save a bullet.
Sprint into cover 10 times while under fire. (campaign only)
Buck the chain of command.
Kill 75 enemies with any shotgun. (campaign only)
Kill an enemy by tagging him with a sticky grenade. (campaign only)
Play it loose.
Kill an enemy just as they are throwing a grenade. (campaign only)
Face the horrors of war.
Kill an Edged Weapon Expert while he is up to 5 meters away. (campaign only)
Kill 4 enemies with a shotgun in 10 seconds or less. (campaign only)
Kill 5 enemies using blind fire. (campaign only)
Engineer an exit strategy.
Kill 3 enemies with a single grenade. (campaign only)
We have contact.
Complete three chapters in a row without being killed or reloading a checkpoint.
Look out below.
Recover one Intel Item.
What's lost is found.